• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.3C
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• pp.127-136
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• 2009

The objective of this study is the development and verification of the 4-electrode resistivity probe (4ERP) for the estimation of electrical properties of the saturated soils. The 4ERPs with wedge and plane types are manufactured to obtain the electrical resistivity without polarization at the electrodes by using Wenner array. The wedge type is for the penetration into the soil samples and the plane type is for the installation into the cells used for the laboratory tests. The consolidation tests are carried out by using 6 types of glass beads and 3 types of sands in size. The test results show that the electrical resistivity increases with a decrease in the porosity, and the constant m used in Archie's law is dependent on the particle shape rather particle size. The one dimensional liquefaction tests show that the porosity obtained by the 4ERP is similar to that determined by the volume fraction. The penetration of the 4ERP into the large scale calibration chamber produces the resistivity profiles. This study demonstrates that the 4ERP may effectively estimate the porosity of the saturated soils.

• Journal of the Korean Ceramic Society
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• v.26 no.2
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• pp.258-266
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• 1989

The effects of grain size and dopant ZnO on the photoelectrochemical conversion in TiO2 ceramic electrodes have been investigated. The photocurrent increases with increasing grain size in the undoped TiO2 ceramic electrode. In ZnO-doped TiO2 electrodes, the photocurrent decreases with increasing ZnO up to 0.4 wt% due to decrease of donor concentration, and then with further addition of ZnO, photocurrent increases according to the formation of second phase. However, the photoresponse appears at wavelength of 420nm, which is very close to the energy band gap of TiO2, regardless of grain size and amount of ZnO.

• Korean Journal of Materials Research
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• v.14 no.8
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• pp.587-594
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• 2004

Three-dimensionally ordered macroporous (3DOM) structures of the $LiCoO_2$ electrode materials for Li secondary batteries were fabricated by using the close-packed arrays of PMMA spheres served as templates. In order to successfully fabricate the cathode materials with highly ordered array form, the metal citrates were applied to new precursors. The precursor/template composites were prepared by the infiltration with metal citrate precursors into the voids of template. By removing the PMMA templates, then, the inverse opal structures with the uniform pores of narrow size distribution were resulted. It was confirmed that the 3DOM $LiCoO_2$ material is to take a single phase of rocksalt (R3m) structure. In addition, 3DOM $LiNiO_2$ and $LiMn_{2}O_4$ cathode materials were fabricated using an identical preparation procedure. Also, the morphology of the 3DOM cathode materials calcined at $500^{\circ}C\;to\;700^{\circ}C$ was observed by scanning electron microscope.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.9
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• pp.427-432
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• 2005

Ion migration characteristics of a rotary spark airgap of high voltage Pulse generator had been investigated. It was considered that the ion migration speed and the ions of the gases(atmosphere gases, $O_2,\;N_2,,\;and\;H_{2}O,\;etc$.) and the charged very fine particles(about $10\~100nm$ size) migrated through the upper stator ball and bottom stator ball of the rotary spark airgap would determined the rise and fall times of the output high voltage pulse. In this paper, a basic study on the ion migration characteristics of the rotary spark airgap between the spark stator ball and the ion-sensing electrode of the proposed high voltage pulse generator have been investigated experimentally. As a result, the three kinds of ion speeds were detected by the ion-sensing electrode installed at the position of the bottom stator ball of the ball type sparkgap high voltage pulse generator. The migration velocities, diameters, masses, charges, numbers of the ions and particles were obtained by experiments and calculations, which, however, would determine the rise and fall times of the output high voltage pulse.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.59 no.2
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• pp.222-231
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• 2010

This paper presents numerical analysis of measurement errors of ground electrode using the fall-of-potential method. In order to analyze ground resistance error according to the positions of auxiliary probes, firstly, national and international standards were researched. Secondly, numerical ground resistance error of hemispheric electrode was analyzed according to the locations of auxiliary probes and the angle between probes. Then, error-reduced positions of auxiliary probes were shown according to the distance to auxiliary current probe versus ground electrode size. Finally, error compensation method was presented. The results presented in this paper provide useful information regarding ground resistance error of alternative positions of auxiliary probes in case that the auxiliary probes could not be located at the proper position in such cases as there are buildings, roadblock or underground metallic pipe at that position.

• New & Renewable Energy
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• v.4 no.1
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• pp.11-18
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• 2008

In-situ lithiated NiO has been manufactured as a conventional cathode material of molten carbonate fuel cell (MCFC), however this material has a weakness for commercialization of MCFC because NiO is spontaneously dissolved into the electrolyte under MCFC operating conditions, resulting in short circuit between cathode and anode. In this research, therefore, $Co(OH)_2$-coated Ni powder was prepared by precipitation method with controlling pH at low temperature and atmospheric pressure. Modified cathode was fabricated by a conventional tape casting method and sintered at 700$^{\circ}C$ in a $H_2/N_2$ atmosphere, Based on characterization result, Pore size distribution and porosity was suitable for the cathode of MCFC. According to the result of dissolution, Ni solubility of modified cathode was 33% lower than that of conventional cathode. In addition, modified electrode showed a good performance from the single cell operation.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.2
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• pp.155-161
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• 2008

The grounding systems provide a low resistance path for fault or normal currents into the earth. The material for reducing ground resistance is buried around the grounding electrode to increase its effective size of the electrode and thus to obtain low ground resistance. Increasing the contacting area with the grounding electrode is effective for lowering the ground resistance in soils. Using this idea the conductive expansion ground resistance reducing material was developed. In this paper experimental data has shown that the ground resistance reduction method using proposed material is superior to using a typically available commercial ground resistance reducing material.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.267-270
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• 2001

A new small scaling Lateral Trench Insulated Gate Bipolar Transistor (SSLTIGBT) was proposed to improve the characteristics of the device. The entire electrode of the LTIGBT was replaced with a trench-type electrode. The LTIGBT was designed so that the width of device was no more than 10$\mu\textrm{m}$. The latch-up current densities were improved by 4.5 and 7.6 times, respectively, compared to those of the same sifted conventional LTIGBT and the conventional LTIGBT which has the width of 17$\mu\textrm{m}$. The enhanced latch-up capability of the SSLTIGBT was obtained due to the fact that the hole current in the device reaches the cathode via the p+ cathode layer underneath the n+ cathode layer, directly. The forward blocking voltage of the SSLTIGBT was 125 V. At the same size, those of the conventional LTIGBT and the conventional LTIGBT with the width of 17$\mu\textrm{m}$ were 65 V and 105 V, respectively. Because the proposed device was constructed of trench-type electrodes, the electric field in the device were crowded to trench oxide. Thus, the punch through breakdown of LTEIGBT occurred late.

• Journal of the Korean Society for Heat Treatment
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• v.19 no.4
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• pp.219-224
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• 2006

Silver paste with low sintered temperature has been developed in order to apply electronic parts, such as bus electrode, address electrode in PDP (Plasma Display Panel) with large screen area. In this study, nano-sized silver particles with 10-30 nm were synthesized from silver nitrate ($AgNO_3$) solution by chemical reduction method and silver paste with low sintered temperature was prepared by mixing silver nanoparticles, conventional silver powder with the particle size 1.6 um and Pb-free frit. Conductive thick film from silver paste was fabricated by screen printing on alumina substrate. After firing at $540^{\circ}C$, the cross section and surface morphology of the thick films were analyzed by FE-SEM. Also, the sheet resistivity of the fired thick films was measured using the four-point technique.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.413-417
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• 1997

Distributed piezoelectric sensor and actuator have been designed for efficient vibration control of a cantilevered beam. Both PZT and PVDF are used in this study, the former as an actuator and the latter as a sensor for our integrated structure. For the PZT actuator, the position and size have been optimized. Optimal electrode shape of the PVDF sensor has been determined. For multi-mode vibration control, we have used two PZT actuators and a PVDF sensor. Electrode shading of PVDF is more powerful for modal force adjustment than the sizing and positioning of PZT. Finite element method is used to model the structure that includes the PZT actuator and the PVDF sensor. By deciding on or off of each PZT segment, the length and the location of the PZT actuator are optimize. Considering both of the host structure and the optimized actuators, it is designed that the active electrode width of PVDF sensor along the span of the beam. Actuator design is based on the criterion of minimizing the system energy in the control modes under a given initial condition. Sensor is designed to minimize the observation spill-over. Modal control forces for the residual(uncontrolled) modes have been minimized during the sensor design. Genetic algorithm, which is suitable for this kind of discrete problems, has been utilized for optimization. Discrete LQG control law has been applied to the integrated structure for real time vibration control. Performance of the sensor, the actuator, and the integrated smart structure has been demonstrated by experiments.